fix fortran + ARM 64 bits.

fix fortran + ARM 64 bits.
I would like to get rid of these lists of architectures, and rely on cmake sizeof_voidp ... but this would mean relying on internal_config from smpi.h, and this is bad practice in simgrid :p Any idea ? Feel free to change it.
Anyway I changed the one in a cpp file that handles 99% of the cases, le .h is there for some ugly corner cases... This should not trigger too many errors in case of a new 64bits architecture popping.